Oscillator coil system for low frequency bands



J. D. REID 2,145,371

OSCILLATOR COIL SYSTEM FOR LOW FREQUENCY BANDS I Jan. 31, 1939.

Filed Dec. 31,

kwmgumwxgkk M w 3nnentot Patented Jan. 31, 1939 UNITED STATES OSCILLATOR COIL SYSTEM FOR LOW FREQUENCY BANDS John D. Reid, Philadelphia, Pa., assignpr to Radio Corporation of America, a corporation of Delaware Application December 31, 1936, Serial No. 118,633

Claims.

The present invention relates to oscillators for multiple wave band radio receivers, and more particularly it relates to an oscillator coil system for the low frequency bands to which the 5 receiver may be tuned.

It is an object of the present invention to provide an oscillator coil system for certain frequency bands, such as the broadcast and weather report bands commonly known as the A and X bands, respectively, whereby the initial frequency adjustments may be made substantially permanent and not subject to misalignment after an extended period of use or in the process of handling the apparatus in which the oscillator is included.

A problem encountered in modern receiver design is that involved in causing the variable tuning capacitors in connection with the oscillator first detector and radio frequency amplifier to track or operate in proper alignment with each other throughout a predetermined tuning range or wave band when interconnected for gang or unicontrol operation. It is customary to operate the tuning capacitors in connection with a common operating shaft, and, in providing an oscillator circuit in connection with one of the tuning capacitor sections, series tracking or tuning capacitors are provided in circuit with the main variable capacity, in order that the oscillator frequency may bear a predetermined relation to the signal frequency throughout the tuning range.

In certain lower frequency tuning ranges, difficulty has been experienced in the adjustment of the oscillator circuits, for the reason that the series tuning capacitors for the oscillator circuit are required to be of the same order of capacity as the maximum capacity of the main variable tuning capacitor employed in the circuit, and a small percentage capacity variation in the series tracking capacitor appreciably affects the tuning response of the oscillator circuit.

With compression mica capacitors provided as series tuning or tracking capacitors, frequent alignment in use is required, because of temperature and humidity changes affecting the capacitors and oscillator alignment in certain low frequency bands, such as the X and A bands referred to, which have the above relation in capacity between the series and main tuning 5) capacitors.

It is, therefore, a further object of the present invention to provide an improved oscillator coil system whereby the oscillator circuits may accurately be aligned in the tuning bands wherein the series and main. tuning capacitors are of the same order of capacity and maintained in alignment without resorting to variable trimmer capacitors.

It is also a further object of the present invention to provide an oscillator coil system in a multiple wave band receiver wherein the series or tracking capacitors in the oscillator circuit may be fixed in value and which may further be manufactured with wider tolerances in the range of capacity variation from a standard than has heretofore been possible.

In accordance with the invention, the oscillator of a superheterodyne receiver is provided with a multiple unit coil system, one unit of which is provided for the lowest frequency band, a second unit for a plurality of intermediate wave bands, and a third coil unit for the highest frequency band.

Furthermore, the series tracking adjustment for each of the lowest frequency and next to the lowest frequency bands takes the form of adjustable magnetite cores for the coils, whereby the coils are adjustable in inductance value as a low frequency adjustment for each tuning band, thereby permitting the use of fixed series tracking capacitors without requiring extremely close tolerance in the capacity values thereof. In combination with this type of circuit, a variable air dielectric trimmer capacitor is provided for adjusting the tuning at the high frequency ends of the Wave bands.

The invention will, however, be better understood from the following description, when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing,

Fig. 1 is a schematic circuit diagram of an oscillator for a multiple wave band receiver embodying the invention, and

Fig. 2 is a view partly in cross-section and substantially full size of an oscillator tuning coil, as provided in the circuit of Fig. 1, showing the method of adjusting the low frequency end of the tuning range for one frequency band.

Referring to Fig. 1, 5 is an oscillator tube having a cathode 6, provided with a heater 1, an output anode 8, a suppressor grid 9, a screen grid [0, and a control grid II. This may be of the metal tube type, such as an RCA 6J7 tube.

The grid H is connected through a grid leak and capacitor |2-l3, with an input circuit lead M which is permanently connected with the stator of a tuning capacitor section [5, the rotor of which is grounded, as indicated at l6. Further connection for the input lead is provided through a Wave band selector switch II, with high potential terminals l8, I9, 20 and 2| of the various wave band tuning coils 22, 23, 24 and 25 for the oscillator. These connections are provided selectively through a movable contact arm 26, which, in the fifth position in a clockwise direction of rotation, connects the input circuit with an ultra high frequency band coil 21.

The coils 23, 24 and 25 are wound on a common form 28 as shown in Fig. 2, to which attention is now directed along with Fig. 1 and in which figure the same reference numerals designate like parts as in Fig. 1. The coil form is mounted in the chassis represented at 29 vertically through an opening 50 with the lower terminal end 3| depending within the chassis and with the upper end enclosed by a metallic shield casing 3| secured to the chassis and forming a support for the coil form through brackets indicated at 32. The coils 23, 24 and 25 are provided on the same form, as a unit, with the lowest frequency coil at one end.

A sleeve 33 within the coil form is provided as a guide for movable cylindrical core 34 of magnetite material for adjusting the inductance of the winding 23 for the A or lowest frequency band. The adjustment is effected by a threaded rod 35 extending axially from the center of the shield can through a threaded bushing 36, and connected at its inner end with the core 34'.

The magnetite core is of natural ferrous material and therefore introduces a variation in the inductance of the winding 23 as it is moved with respect to it, along the axis, the inductance of the winding being increased as the core is moved downwardly and closer to the winding to reduce the reluctance of the space within the winding.

The windings 24 and 25 are substantially unaffected by this adjustment. This inductance adjusting arrangement is also provided in connection with the winding 22 in a similar manner and for the same purpose, as will hereinafter be pointed out.

With the switch in the position shown, the input circuit lead 14 is connected through the contact arm 25 with a contact 40 having a connection lead 4| to the coil in which is located a tracking or series tuning capacitor 42, to in clude the latter in circuit between the high potential terminal 18 and the tuning capacitor I5. The series tuning capacitor 42 may have a value of substantially 180 micromicrofarads for a frequency band such as the X band, tuning from 150 to 410 kc. with a main tuning capacitor section I5, having a tuning range of from 11 to 480 micromicrofarads, as indicated.

The variable tuning capacitor unit of which the capacitor i5 is a part for gang or multiple operation, includes tuning capacitors 43 and 44 for the radio frequency and first detector circuits, and may be operated therewith by any suitable common tuning control means represented by a tuning dial, indicated at 45.

In order that these capacitors may track or provide proper alignment and signal response throughout the various tuning bands, each circuit must be accurately aligned at the high and low frequency ends of each tuning range and for this purpose the series tracking capacitor 42 is ordinarily made adjustable for the low frequency end of the tuning range, and a shunt variable tuning capacitor indicated at 46 is provided for adjusting the high frequency end of the tuning range, the adjustment being facilitated by providing a fixed capacitor 41 in parallel with the variable capacitor, as shown. The anode end of the coil and the trimmer capacitors 36 and 41 are connected to ground as indicated at 48 to complete the tuned circuit.

As the oscillator shown is of the Hartley type the tap 49 on the tuning inductance is connected to the cathode of the oscillator, and in the prescut example the other cathode connections for the The A band inductance 23 is connected to the input circuit [4 of the oscillator grid through a contact 55 to which the arm 25 is movable for selecting the A band adjustment, and a connection lead 56 in which is located the series tracking capacitor 51 for the A band. This may have a value of 555 micromicrofarads and provides a series capacity between the high potential terminal 19 of the A band inductance and the grid circuit including the tuning capacitor section 15.

Like the X band coil, the A band coil 23 is provided with a shunt variable trimmer capacitor 58 and a fixed capacitor 59 for adjusting the frequency response at the high frequency end of the tuning range and the low frequency end of the range is adjusted by means of the variable core 34. A similar core 34a is shown in connection with the X band coil 22 and is adjusted in the same manner as the A band core to provide a proper resonance at the low frequency end of the tuning range when the capacitor I5 is operating in the X band.

It will be noted that the A band coil 23 and the trimmer capacitors 58 and 59 are also connected to ground as indicated at 5!. The screen grid Ill serves as an anode electrode feeding back to ground 62 through a by-pass capacitor 63 across the anode circuit resistor 54.

As the wave band adjustments do not concern the present invention in detail, the same are not believed to require further description. However, it may be pointed out that, because of the wide difference in capacity between the series tracking capacitors for the B and C bands with respect to the capacity of the variable tuning unit [5, slight variations in manufacture of the series tracking condenser have no appreciable effect upon the tuning adjustment. In the C band the tracking capacitor, indicated at 55, may have a capacity of substantially 4800 micromicrofarads while that for the B band, indicated at 66, may have a capacity of approximately 1500 micromicrofarads. It will, therefore, be seen that a slight variation in capacity of the series tracking condenser may be a relatively small percentage of the total capacity effective to cause inaccuracy in tuning with the unit l5.

The A band coil is tunable over a frequency range of substantially 530 to 1800 kc. by the same tuning capacitor unit l5 as is used for the X band, and it will be seen that the series tracking capacitor 5! has a capacity of the order of that of the main tuning unit. This is sufiiciently close to the capacity range of the unit l5 that slight variations may provide large percentage variations of tuning. Such variation is prevented from being efiective in this circuit and the X band circuit, by fixing the value of the capacitors 42 and 51 at a value having a tolerance variation of substantially 5% from the nominal design Values given, and providing further tuning by the adjustable cores 34' and 34a to provide a proper low frequency alignment in each of the tuning bands of the oscillator having the above order of capacities in the tunable circuits.

In manufacture, the low frequency series capacitors 42 and 51, heretofore consisting of multiple-plate air-dielectric capacitors or multiplelayer compression type mica, are entirely eliminated and in place thereof wide tolerance fixed capacitors are substituted to tune the circuits. Further tuning for exact alignment, at 600 kc. and 175 kc, for example, on the A and- X bands, respectively, is obtained by changing the inductance of the tuned circuits by means of the cores. Since the cores are cylindrical and susended by a screw adjustment, not under tension, the alignment is substantially permanent and may be fixed by any suitable means in connection with the adjustment screw 35, such as a spring washer indicated at T0 in Fig. 2. Adherence to capacity values is made certain by sealing the series capacitors, which is made possible by this tuning arrangement.

By placing the A'band coil at the one end of the winding and mounting that end at the top with the coil form in a vertical position, additional coils or windings for the intermediate bands may be accommodated, as shown in Fig. 2, and with a saving in space on the chassis, and without interfering with the tuning adjustment.

While the invention has been shown and described connection with tuning an oscillator circuit in two bands now in common use in receivers such as the 150-410 kc. X band and the 5394800 kc. A band, for an intermediate frequency of 460 kc., the tuning system may be used in connection with any oscillator circuit for tracking adjustment when the series and main tuning capacitors are required to have capacity values of substantially the same order.

For example, if higher than 460 kc. intermediate frequency output is required, the series tuning capacitors for the higher frequency bands may become of the same order as the common tuning capacitor. In the case of an intermediate frequency of 4600 kc., for example, the series tuning or tracking capacitor may have a value of 480 micromicrofarads for the C band of from 6800- 22,000 kc., or approximately one-tenth its present value for an intermediate frequency of 460 kc.

I claim as my invention:

1. In a tunable oscillator system for a plurality of frequency bands including two low frequency tuning bands, the combination of tuned oscillator circuits comprising tuning inductances, a variable tuning capacitor and fixed series tuning capacitors, said last named capacitors each being of the order of the total capacity of the variable tuning capacitor and being fixed at a value which lies within a range of predetermined capacities having relatively wide limits, means for effecting a low frequency adjustment for each of said tuning bands, comprising a magnetite core in at least one of said tuning inductances, and means for moving said core to adjust the value of said tuning inductance.

2. An oscillator circuit for a multiple wave band radio receiver comprising a coil system having inductance elements comprising tunable windings for two low frequency tuning bands, a common tuning capacitor for said windings, means for selectively connecting said tuning capacitor with each of said windings, a series tuning capacitor in each of said connections for approximately determining the low frequency limit of the tuning range in each of said bands, and a magnetite core movable with respect to each of said inductances to vary the inductance thereof and to complete the adjustment of the low frequency limit of the tuning range in each of said bands.

3. An oscillator circuit for a multiple wave band radio receiver, comprising a coil system having an inductance element comprising two tunable windings for a low frequency tuning band, and an adjacent tuning band, a common tuning capacitor for said windings, means for selectively connecting said tuning capacitor with each of said windings, a series tuning capacitor in each of said connections for approximately determining the low frequency limit of the tuning range in each of said bands, and a magnetite core movable with respect to and associated with each of said inductances to vary the inductance thereof and to complete the adjustment of the low frequency limit of the tuning range in each of said bands, said core members being cylindrical and having a screw thread adjustment whereby they are movable axially with respect to the inductance elements, and means for locking said cores in adjusted position.

4. An oscillator coil system for multiple wave band radio receivers and the like, including in combination, a plurality of inductance windings, a main variable tuning capacitor comprising a section of a multiple tuning unit, an oscillator tube having a control grid connected with said tuning capacitor section, a switch for connecting said tuning capacitor section and said control grid selectively with the high potential ends of said tuning inductances, a series tuning capacitor for two of the tuning bands connected between said high potential terminal and the tuning capacitor section in each circuit for aligning the tracking of said tuning capacitor section with the remainder of the tuning unit, said capacitors being sealed and fixed to capacity values of the order of the value of the tuning capacitor section, and means for completing the low frequency tuning adjustment of said circuits comprising a magnetite core movable with respect to the axis of the tuning inductances of said two tuning bands.

5. In a multi-wave band oscillator for a radio receiver, means providing a common tuning capacitor for said receiver including a capacitor for tuning said oscillator, a plurality of inductance windings selectively connectable with said tuning capacitor, means for tuning said inductance windings to provide circuit alignments at the high frequency end of each tuning band comprising a shunt air dielectric variable capacitor across each winding, a series tuning capacitor in circuit with each winding to provide a frequency adjustment at the low frequency end of each tuning band, and means for completing the adjustment of the limit of the tuning range at the low frequency end of each of two lower frequency tun.- ing bands, comprising a movable magnetite core for the tuning inductances thereof to vary the inductance thereof within a predetermined range, including a variation range to compensate for variation in the capacity of the series capacitors from a predetermined value, and means for looking said cores in adjusted positions.

JOHN D. REID. 

